Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Reconciliation of the Difference between the Benefit for Income Taxes and Income Taxes at the Statutory U.S. Federal Income Tax Rate

A reconciliation of the difference between the benefit for income taxes and income taxes at the statutory U.S. federal income tax rate is as follows for the years ended December 31, 2015, 2014, and 2013 (in thousands, except percentages):



	2015					2014					2013
	Amount			% of Pretax Earnings		Amount			% of Pretax Earnings		Amount			% of Pretax Earnings
Income tax benefit at statutory rate	$	(39,907	)	34.0	%	$	(20,166	)	34.0	%	$	(12,392	)	34.0	%
State income taxes	(2,176		)	1.9	%	(1,343		)	2.3	%	(852		)	2.3	%
Research and development credits	(5,698		)	4.9	%	(2,577		)	4.3	%	(2,265		)	6.2	%
Foreign rate differential	2			—	%	—			—	%	—			—	%
Permanent items	3,687			(3.1	)%	1,525			(2.6	)%	3,060			(8.4	)%
Provision to return adjustments	(426		)	0.2	%	64			(0.1	)%	320			(0.9	)%
Effect of change in state tax rate	932			(0.8	)%	2			—	%	(1		)	—	%
Increase in unrecognized tax benefits	950			(0.8	)%	425			(0.7	)%	566			(1.5	)%
Change in valuation allowance	42,636			(36.3	)%	22,070			(37.2	)%	11,564			(31.7	)%
Net benefit	$	—		—	%	$	—		—	%	$	—		—	%

Components of Deferred Tax Assets and Liabilities

The components of deferred tax assets and liabilities at December 31, 2015 and 2014 were as follows (in thousands):



	December 31,
	2015			2014
Deferred tax assets:
Domestic net operating loss carryforwards	$	93,923		$	59,312
Foreign net operating loss carryforwards	2			—
Research and development expenses	1,289			405
Capitalized Section 174 expenses	51			57
Research and development credits	8,889			4,572
Accrued bonuses	822			1,066
Share-based compensation	3,671			1,045
Other	604			135
Total gross deferred tax assets	109,251			66,592
Valuation allowance	(109,111		)	(66,475		)
Total deferred tax assets	140			117
Deferred tax liabilities:
Other	(140		)	(117		)
Total deferred tax liabilities	(140		)	(117		)
Total deferred tax assets and liabilities, net	$	—		$	—

Summary of Uncertain Tax Benefit

Therefore, the Company recognized an uncertain tax benefit associated with the federal R&D credit carryover during the years ended December 31, 2015 and 2014, as follows (in thousands):



Balance at December 31, 2013	$	581
Increases related to 2014	425
Increases related to prior periods	—
Balance at December 31, 2014	1,006
Increases related to 2015	940
Increases related to prior periods	10
Balance at December 31, 2015	$	1,956